1. Field of the Invention
The present invention relates generally to filtering apparatus, and more specifically relates to filter units for use in filtering liquids or, more particularly, for use in aquatic environments such as pools, whirlpool-type tubs, and the like. Even more specifically, the invention relates to a replacement filter cartridge assembly.
2. Description of the Prior Art
Many conventional filter cartridge assemblies include a filter cartridge having a filter medium, and a core set permanently in the filter cartridge. A disadvantage of such conventional filter cartridges is that the filter core is not removable from the filter cartridge. Thus, when replacing the filter cartridge assembly, the user discards the core assembly and the filter cartridge.
U.S. Pat. No. 4,108,775 to Wilkes et al. discloses a filter apparatus having an advantage over other conventional units in that the filter apparatus includes a filter cartridge and a core assembly which is removable from the cartridge. As shown in FIGS. 5 and 6 of the Wilkes et al. patent, the filter cartridge includes a pleated filter medium 186 and top and bottom disk-shaped end caps 190, 192 fixed to the ends of the pleated medium. The filter cartridge is formed with a central opening 188 which extends through each end so that the cartridge fits snugly about the core assembly 140.
A disadvantage of the filter apparatus disclosed in the Wilkes et al. patent is that the core assembly provides minimal, if any, longitudinal support for the filter cartridge which may be due at least in part to the core assembly passing through the filter cartridge disk-shaped end caps and engaging the end caps only at their inner peripheral edges which define the opening 188. The pleated medium also does not provide sufficient longitudinal support. Thus, the filter cartridge may be damaged or deformed due to water suction when operating the filter.
Under normal operating conditions in either a pressurized or vacuum skim filter cartridge system, the filter cartridge element is subjected to substantial lateral and longitudinal pressures. These pressures are created by the flow of dirty water through the filter medium and the filtered clean water moving downwardly and exiting the filter housing and returning to the pool. The suction created tends to deform the shape of the filter cartridge. As the filter cartridge becomes dirty, resistance to water flow through the filter increases and greater pressure is exerted longitudinally and laterally on the filter cartridge, which may cause the cartridge to deform or collapse. The distortion in the shape of the filter cartridge may cause water to by-pass the filter medium through areas opened by the distortion. This may allow unfiltered water to reenter the pool.
Further, the distortion of the filter cartridge resulting from the lack of longitudinal support may damage the disk-shaped end caps of the filter cartridge. Thus, the lack of longitudinal support to counter compressive forces leaves the Wilkes et al. filter apparatus susceptible to malfunction.